Darcy's Formula - A formula used to determine the pressure drop due to flow friction through a conduit.

Deliquescent - Moisture is separated by using the absorptive properties of special hygroscopic compounds.

Desiccant - Material that tends to remove moisture from compressed air.

Dew point - The temperature at which vapors in a gas condense. For practical purposes, it must be referred to a stated pressure.

Digital - Of or pertaining to the general class of fluidic devices or circuits whose output varies in discrete steps (i.e., pulses or "on-off" characteristics).

Displacement, volumetric - Volume absorbed or displaced per stroke of a cylinder or per cycle of a pump or motor.

Dissolved air - Air which is dispersed at a molecular level in hydraulic fluid to form a single phase.

Dissolved water - Water which is dispersed at a molecular level in hydraulic fluid to form a single phase.

Dither - A low amplitude, relatively high frequency periodic electrical signal, sometimes superimposed on the servovalve input to improve system resolution. Dither is expressed by the dither frequency (Hz) and the peak-to-peak dither current amplitude.

Droop - The deviation between no flow secondary pressure and secondary pressure at a given flow.

Dryer, compressed air - A device for reducing the moisture content of the working compressed air.

Durometer - 1. An instrument for measuring the hardness of rubber. Measures the resistance to the penetration of an indentor point into the surface of rubber. 2. Numerical scale of rubber hardness.

Efficiency - Ratio of output to the corresponding input.

Elasticity - The property of a material which tends to return to its original shape after deformation.

Elastomer - Any synthetic or natural material with resilience or memory sufficient to return to its original shape after distortion.

Elongation - Generally means "ultimate elongation" or percent increase in original length of a specimen when it breaks.

Emulsion, oil in water - A dispersion of oil in a continuous phase of water.

Emulsion, water in oil - A dispersion of water in a continuous phase of oil.

Emulsifier - additive that promotes formation of a stable mixture, or emulsion, of oil and water.

Emulsion - A homogeneous dispersion of two immiscible liquids, generally of a milky or cloudy appearance.

Entrained air - A mechanical mixture of air bubbles having a tendency to separate from the liquid phase.

Expectancy, life - The predicted working period during which a component or system will maintain a specified level of performance under specified conditions. Sometimes expressed in statistical terms as a probability.